Oil fields are often subjected to waterflooding as a secondary recovery technique wherein water is injected into the oil producing formation to force more oil out of the formation into producing wells than would otherwise be obtained by primary production techniques. When injecting water or other liquids into a geologic formation, it is usually desirable to keep the pressure of the injected water below the pressure at which the formation will fracture. This keeps the flow of injected water out into the formation as uniform as possible rather than preferentially flowing into and through articifically formed fractures or cracks and by-passing substantial parts of the formation.
Heretofore, a technique referred to as a step rate test or formation pressure parting test has been designed to be performed on injection wells for the purpose of determining the fracture pressure of a hydrocarbon-producing geologic formation into which water is pumped for secondary recovery purposes.
Step rate tests are known in the art and are fully and completely disclosed in U.S. Pat. No. 4,192,182, the disclosure of which is incorporated herein by reference. A step rate test requires the injection of water at predetermined ever increasing pressure steps so that the fracture pressure of the formation can be determined. A step rate test requires that at each predetermined pressure, the pressure and water flow rate associated therewith be maintained for a considerable period of time before moving to the next higher pressure and flow rate. In the above cited patent, a portable pumping unit is employed to accomplish the increased steps of pressure and flow rate in order to carry out a step rate test and preferably employs a positive displacement pump well known in the art.